Control and indicator apparatus for rectifiers



Apnl 11, 1950 N. c. OLMSTEAD comm. AND INDICATOR APPARATUS FOR RECTIFIERS Filed Dec. 21, 1946 INVENTOR 8y MC. OLMSTEAD 75 W ATTORNEY Patented Apr. 11, 1950 CONTROL AND INDICATOR APPARATUS FOR RECTIFIERS Noel C. Olmstead, Morristown,

Bell Telephone Laboratories,

N. J., assignor to Incorporated, New

York, N. Y., a corporation of New York 1 Application December 21, 1946, Serial No. 717,724

5 Claims. (Cl. 321-43) This invention relates to electric control and indicating apparatus particularly for rectifiers. More specifically, the invention relates to apparatus for interrupting the energization of a rectifier when abnormal operation of the rectifier occurs and for identifying the rectifier element which caused the abnormal operation.

An object of the invention is to provide improved apparatus for controlling the energization of a rectifier.

Another object is to provide means for identifying the space current rectifying device of a plurality of suchrectifying devices in which reverse current fiow first occurs.

In a mercury vapor tube rectifier, a type of failure frequently encountered is known as areback or back-fire. In this type 01' failure, one or more of the rectifier tubes conducts current in a direction which is reversed with respect to the direction of normal conduction through the tube. Such an arc-back in a rectifier tube may be caused by high tube temperature, age of the tube or by a high transient voltage across the tube electrodes. When an arc-back occurs in a cer tain rectifier tube, that tube and another tube conducting in a normal direction complete a short circuiting path across the current supply source. The resulting abnormally high current flowing in the space current path of the second tube will cause an increase in temperature of that tube so that it, in turn, will probably arc-back on the succeeding part of the powersupply cycle when the polarity of the voltage across the tube electrodes is reversed.

In accordance with a specific embodiment of the invention herein shown and described for the purpose of illustration, thereare provided a multiphase rectifier comprising a plurality of gas or vapor filled space current rectifying devices, a control circuit for controlling the supply of current to the rectifier and a plurality of indicator devices, one for each rectifying device, for identifying the rectifying device in which an arc-back first occurs. For controlling the energization of the control circuit and the selective energization of the indicator devices, there are employed a plurality of auxiliary space current devices, one for each rectifier device and means for generating control voltage pulses for controlling the auxiliary space current devices in response to the flow of reverse currents only through the rectifier devices, respectively.

The means for generating the control pulses comprises a plurality 'of transformers, one for each rectifier device, each having a saturable core, a primary through which fiows the space current passing through the associated rectifier device, and asecondary across which the control voltage pulses are set up. An important feature of the invention is the provision of means for producing in each transformer core a unidirectional magnetomotive force for setting up a saturating fiux in the core which magnetomotive force is in aiding relationship with respect to the magnetomotive force produced in the core due to the primary current flowing in the normal direction through the associated rectifying device. Specifically, this saturating flux is set up by a direct current supplied to the secondary of the transformer. If the core were unsaturated or if the core were saturated only by current flowing in the primary winding, a pulse of one polarity would be produced in the secondary when the normal current in the primary rises quickly from zero to full value at the start of a conduction period of a rectifier tube and a pulse of opposite polarity would be produced in the secondary when the primary current is interrupted at the end of each conduction period or when conduction in the reverse direction is started through a rectifier tube due to an arc-back. Under these conditions, therefore, an auxiliary pulse operated space current device would be unable to distinguish between pulses generated in response to the normal current flow through a rectifier tube and its transformer primary and a pulse generated due to current flowing in a reverse direction through a rectifier tube and its associated primary when an arc-back occurs in the rectifier tube. However,

when the core is saturated independently of the current fiowing in the primary of the transformer due to amagnetomotive force which aids the magnetomotive force set up by the normal primary current, no pulse or a pulse of negligibly small amplitude is produced in the secondary in response to the alternate starting and stopping of normal rectified current flowing in the primary and a current pulse of substantial magnitude is set up in the secondary only when a reverse current fiows in the primary, that is, when an areback. occurs in a rectifier tube, this reverse cur-,

rent setting up in the core a magnetomotive force which opposes the .magnetomotive force which produces the saturating flux, thus causing the core to become unsaturated. This opposing magnetomotive force may be of the same order of magnitude or greater than the magnetomotive force which produces the saturating flux, for example, so that the resulting flux is reduced substantially to zero or reversed in direction when 3 reverse current flows through the rectifier tube.

The invention will now be described in greater detail with reference to the accompanying drawin the single figure of which is a schematic view of a rectifier embodying the invention.

The drawing shows a three-phase high voltage rectifier comprising two electrode, mercury vapor filled rectifier tubes l l, I: and i3, and a transformer M, for rectifying current from a threephase alternating current supply source 95, and for supplying the rectified current to a load it. While a three-phase rectifier is shown in the drawing, a rectifier having any number of phases may obviously be employed. The rectifier is started in operation by closing the switch it which causes current from a direct current mil-volt source, shown as a grounded battery 5 t, to be supplied to the winding of a relay l9, thereby causing an energizing circuit to be completed from the current source it: to the delta connected primary windings of transformer is. Terminals of the secondary winding of transformer M are connected to the anodes of rectifier tubes ii, i2 and 53, respectively, and a common terminal of the secondary windings is connected to the negative load terminal. The cathodes of tubes it, i2 and i3 are connected to the positive load terminal, suitable means, not shown, being provided for supplying heating currents to the cathodes. The operation of relay is also causes the completion of a circuit for charging a condenser 28 (8 microiarads) by current from source 58 through a circuit comprising a series resistor megohm).

There are provided three similar impulse transformers ii, 22 and 23, each comprising a toroidal core 25 preferably of Permalloy ribbon or other magnetic material having a high permeability at low magnetizing forces and which is easily saturated, a single wire primary 25 passing through the toroid substantially along its axis, and a secondary 26 of a large number of turns. As shown in the drawing, the primary 25 is a lead connecting the cathode of a rectifier tube to the positive load terminal but it could as well be a lead which connects a terminal of a secondary winding of transformer it to the anode of a rectifier tube. Insulation is provided by the air space between the primary wire 25 and the toroidal core 24, or, if desired, a bushing of ceramic material may be provided for insulating the primary lead from the core. Direct currents from source it are supplied to the secondary windings 26 of transformers El, 22 and 23, respectively, through circuits comprising series resistors 34, and 36, respectively, each of 56,000 ohms, one terminal of each resistor being grounded. The direct currentof about 2 milliamperes flowing through the winding 2% of transformer H, for example, causes to be set up in the core 24, a unidirectional fiux for saturating the core.- The core has the characteristic that the saturation point is reached very abruptly, that is, the knee of the magnetization curve is very sharp. The current in winding 26 is adjusted to bring the flux in the core to a point just above the knee of the magnetization curve. The current flowing in a normal direction from the anode to the cathode of a rectifier tube and through the primary lead 25 sets up a magnetomotive force in the core 2| which is in a direction to aid the magnetomotive force set up in the core by the direct current flowing through the secondary winding 28. However, the core is saturated due to th current in winding 26 to such an extent that the additional magnetomotive .4 a force due to the normal current in primary 28 produces no appreciable increase influx in the core 24. Therefore, when a normal current starts to flow through a primary lead 25 due to the anode of an associated rectifier tube becomin positive with respect to its cathode, or when the current through the rectifier tube is subsequently interrupted due to a reversal of polarity of the rectifier tube electrodes, no appreciable change of fiux occur in the core 25 and no pulse of appreciable amplitude will be induced in the secondary winding 26. However, when an arcback occurs in a rectifier tube causing it to conduct current in the reverse direction, this reverse current in the primary 2%; sets up in core 2d a magnetomotive force the magnitude of which may be substantially equal to or even greater than that of the magnetomotive force set up by the current in winding .26, the two mag-=- netomotive forces being opposed. When the amplitude of the reverse current in the primary increases to cause the flux in the core to decrease, and possibly to fiow in the revers direction an impulse of one polarity will be induced in the secondary winding 25 and when the reverse current subsequently decreases to cause the flux in the core to increase, an impulse of opposite po larity is induced in the secondary winding.

There are rovided three gas-filled space current tubes 3!, 32 and 33 (type 2D21), known as thyratron tubes, associated with the transformers 2H, 22 and 23, respectively, each tube having an anode, an indirectly heated cathode, a screen grid and a control grid. The anodes of tubes Si, 32 and 33 are connected through the winding of a relay 3?, through the armature and contact of a relay S8 and through switch ll to the positive terminal of direct current source it. Three voltage divider circuits are connected across the battery 58, one comprising resistors 50 and iii, a second comprising resistors 52 and 53 and the third comprising resistors 5d and 55. Resistors 5d, 52 and 53 each have a resistance of 33,000 ohms and resistors 5!, 53 and 55 each have a resistance of 3,900 ohms. The screen grid and cathode of tube 3! are connected to a common terminal of resistors 50 and ti, th screen grids and cathodes of tubes 32 and 33 being similarly connected to the common terminal of resistors 52 and 53 and to the common terminal of resistors 5t and 55, respectively. The common terminal of secondary transformer winding 29 and of resistor 35 is connected through a condenser as to the control grid of tube 3!, a common terminal of the secondary winding of transformer 22 and of resistor 35 bein similarly connected through a condenser 51 to the control grid of tube 32 and a common terminal of the secondary winding of transformer 23 and of resistor 36 being connected through a condenser 58 to the control grid of tube 33. The control grids of tubes 3 I, 32 and 33 are connected through one megohm resistors 59, 60 and SI, respectively, to ground.

Three cold cathode, gas-filled indicator tubes 4!, 42 and 43 (type 359A) each having a main anode, a control electrode and a cathode, are provided for producing a visible glow in one of the tubes when current flows in the space separating its main anode and the cathode. The contro electrodes of tubes ti, 52 and 43 are connected through 1 megohm resistors 44, 55 and 4B, to the cathodes of tubes 3|, 32 and 33, respectively. The anodes of indicator tubes 4!, 42 and 53 are each connected through a switch 62 to the rmsitive terminal 01 battery l3 and the cathodes oi tubes 4|, 42 and 43 are each connected through a common resistor 41 of 3,300 ohms to ground.

During normal operation of the rectifier, the control grids of tubes 3 I 32 and 33 are each maintained at ground potential due to the paths to ground through resistors 59, 53 and 6| and the cathodes of the tubes are maintained at a potential of 12 volts positive with respect to ground due to the potential difference across each of resistors 3|, 53 and 55. If an arc-back occurs in rectifier tube ||,'for example, and as a result current com mences to fiow through primary lead 25 in a direction which is revers d with respect to the normal direction of current flow, there is induced in the secondary transformer winding 23 and impressed upon the control grid-cathode circuit of tube 3| a, voltage pulse of such polarity and amplitude that current conduction is started in the space separating the anode and cathode of tube 3|. As a result the anode to cathode potential drop in the tube 3| is reduced to about 8 volts and the potential of the cathode with respect to ground is increased to about 112 volts. The space current flowing in tube 3| is limited to about 25 milliamperes by the resistance of the winding of relay 31 and by the resistor The potential of 112 volts at the cathode of tube 3| is applied to the control electrode of indicator tube 4| to cause conduction to be started in the space separating the control electrode and cathode. The control electrode-cathode current in tube 4| is limited to about 100 microamperes by the resistor 44. This current conduction in the control gap separating the control electrode and cathode of tube 4| causes the main gap separating the anode and cathode to conduct current and thereby produce a visible blow in tube 4| to indicate that an areback has occurred in rectifier tube The voltage drop across the anode and cathode of tube 4|, when conducting, is '70 volts and therefore the potential at the cathodes of tubes 4|, 42 and 43, is increased to 50 volts. Even if one or both of tubes 32 and 33 should become conducting due to an arc-back in rectifier tube l2 or l3, or both, after tube 3| commences to conduct space current to cause the control electrode potential of tube 42 or 43, or both, to be increased to 112 volts, the potential difference between the control electrode and cathode of tube 42 or 43, or both, will be in suificient to initiate current conduction in these tubes. Therefore, one only of the indicator tubes 4|, 42 and 43 becomes conducting to identify the rectifier tube in which abnormal or reverse conduction first occurred so that the rectifier tube may be replaced. To restore the indicator tube 4| to the non-conducting condition, the switch 62 may be opened, the circuit then being restoredto normal by reclosing switch 62.

Current conduction in tube 3|, for example, in addition to causing the energization of indicator tube 4|, also causes the energization of relay 31 which operates to remove energizing current from the winding of relay IS. The resulting release of relay I9 opens the circuit for supplying alternating current from source I5 to the primary of transformer l4 of the rectifier. Power is thus quickly removed from the rectifier following the occurrence of an arc-back in a rectifier tube before the rectifier equipment can become damaged. The release of relay l9 also causes the completion of a circuit for supplying energizing current from source It! to the winding of relay 33, the energizing current flowing through the anodecathode path of a cold cathode tube 63, like tubes 4|. 42 and 43, to ground. The tube 33 has previously been conditioned for conduction due to the voltage across the charged condenser 23 which is impressed upon the control electrode-cathode circuit of tube 63, this circuit including a series resistor 34. The operation of relay 33 opens the energizing circuit for relay 31 to thereby interrupt the current conduction in tube 3| and to again cause energizing current to be supplied to relay IS. The operation of relay |9 completes a circuit for supplying alternating current to the rectifier, opens the circuit for energizing relay 33 and completes a circuit for charging condenser 23 through series resistor 29. The starting circuit is thus restored to the condition it was in before the arc-back occurred in tube 3|. Thus whenever an arc-back occurs, the source of anode voltage for the rectifier tubes will be disconnected and immediately restored provided only that condenser 23 is charged to the voltage required for causing conduction in the control electrode-cathode circuit of tube 63. The operation of relay 33 completes a I discharge path for condenser 23 through a resistor 65 of ohms to insure that enough time must elapse after operation of relay 31 to recharge condenser 23 in order that an automatic reclosing of the energizing circuit for the rectifier may be elfected. If an arc-back should recur within a period of less than a certain minimum duration following the operation and the subsequent release of relay IS, the condenser 23 will be charged to a voltage less than that required for rendering the tube 63 conducting. In that case relay 33 will not be operated, relay 3! will therefore not release and relay l9 will fail to operate. In order to then restart the circuit it will be necessary to open and then reclose the switch II. By making the resistance of resistor 34 greater than that of resistor 29 the discharge of condenser 28 through the control electrodecathode circuit of tube 63 will be at a lower rate than the rate of charging condenser 23 through resistor 29 so that the tube 63 and the associated circuit will not act as a relaxation oscillator.

What is claimed is:

1. In combination with a rectifier comprising a space current rectifying device of a relay means for connecting said rectifier to an alternating current supply source when said relay means is energized, means responsive to an arc-back or reverse current fiow in said rectifying device for causing the deenergization of said relay means to cause said rectifier to be disconnected from said alternating current supply source and means responsive to the deenergization of said relay means only when the preceding energization period of said relay means has been greater than a certain minimum period for causing the reenergization of said relay means to cause said supply source of alternating current to be reconnected to said rectifier.

2. In combination with a rectifier comprising a space current rectifying device of a first relay for completing a circuit for supplying current from an alternating current supply source to said rectifier when said relay is energized, a condenser and a resistor in series, said first relay when energized, completing a circuit for charging said condenser through said resistor by current from a direct current source, a second relay for interrupting the energizing circuit for said first relay when said second relay is energized, means responsive to a reverse current flow through said rectifying device for causing the energization of said third relay is energized, means for completing a discharge path for said condenser in response to the operation of said third relay and means responsive jointly to the voltage across said condenser when sufficiently charged and to the release of said first relay for causing the energization of said third relay.

3. In combination, a multiphase rectifier comprising a plurality of space current rectifying devices, a circuit comprising said rectifier for supplying rectified current from an alternating current supply source to a load, a plurality of transformers each having a core of magnetic material, a primary and a secondary, said primaries being connected in series with said rectifying devices respectively, means for producing a saturating flux in each of said cores independently of the normal rectified currents flowing in said primaries, respectively, the magnetomotive force producing the saturating flux in the core of each transformer being inaiding relationship with respect to the magnetomotive force produced by the normal current flowing in the primary of the transformer, a reversed current flow in the priwary of each of said transformers due to an arc-back in an associated rectifying device causing a large change of flux in the transformer core and thereby inducing a voltage in the transformer sccondary,'means responsive to a voltage induced in any of said secondaries for interrupting and subsequently recornpleting said circuit for supplying rectified current from said source to said load and means responsive to the voltages induced in said secondaries respectively for producing an indication to identify the rectifying device in which said reverse current flow first occurred.

4. In combination, a transformer comprising a core of magnetic material forming a closed flux path, a primary and a secondary, means comprising said secondary of said transformer for setting up in said core a magnetomotive force for producing a unidirectional flux for saturating the core, a current supply circuit comprising in series a source of alternating current, a space current rectifying device and said primary, the current flowing in a normal direction through said rectifying device and said primary causing to be set up in said core a magnetomotive force which aids said first-mentioned magnetomotive force. and a voltage-controlled device responsive to voltage induced in said secondary when the direction of current now in said primary is reversed with respect to said normal direction due to an arc-hack in said rectifying device said voltage-controlled device being unresponsive to any relatively small voltage which may be induced in said secondary in response to a change of current flowing in the normal direction in said primary. v

5. In combination, a transformer having a core of magnetic material, a primary and a secondary, means for setting up a magnetomotive force for producing a saturating flux in said core, a rectifier circuit for supplying rectified current from an alternating current supply source to a load com= prising a space current rectifying device and said primary connected in series in said circuit, the rectified current normally flowing in said primary causing to be set up in said core a magnetomotive force which aids said steady magnetoznotive force and means responsive to a change of flux in said core produced as a result of reversed current flow through said primary and said rectifying device under an abnormal condition for producing an indication of the occurrence of said abnormal condition, said last-mentioned means comprising a plurality of auxiliary space current devices having control circuits associated with said transformer secondaries respectively, said auxiliary space current devices being rendered conductive in response to voltages induced in said secondaries respectively, a plurality of indicating device's associated with said auxiliary space current devices respectively, and means for causing the energization of that indicating device only of said plurality of indicating devices which is associated with the auxiliary space current device in which conduction is first initiated.

NOEL C. OLMSTEAD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

